Compressible Dynamic Stall Alleviation Through High Momentum Blowing

An experiment was conducted in The Ohio State University Transonic Wind Tunnel on a high lift airfoil to evaluate the effectiveness of high momentum steady blowing for dynamic stall control. Computational fluid dynamics (CFD) was used to design airfoil modifications to tangentially inject air behind the leading edge. Extensive design, calibration, and post-test analysis efforts were required to achieve desired flow control system performance and data accuracy. Aerodynamic performance for steady and oscillatory angle-of-attack conditions was measured with the baseline smooth airfoil, with the slot open but no blowing, and with blowing at moderate to high momentum coefficients. The blow-down wind tunnel was operated at Mach numbers between 0.2 to 0.7 and at near full scale Reynolds numbers. High momentum blowing at each Mach number substantially increased airfoil performance, including a 20% increase in maximum lift coefficient for steady conditions at Mach 0.3. For unsteady pitching motions, blowing produced a cycle- averaged lift increase of more than 20% at Mach 0.3 to 0.4. Large reductions in peak adverse pitching moment were also measured in deep dynamic stall. Inadvertently, the experiment incorporated several data points in which suction occurred. These cases also enhanced performance, although to a lesser extent.